<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    let num1 = +prompt('1')
    let num2 = +prompt('2')
    let s = prompt('+-*/')
    switch(s){
        case '+':
        alert(num1+num2)
        break 
         case '-':
        alert(num1-num2)
        break 
         case '*':
        alert(num1*num2)
        break 
         case '/':
        alert(num1/num2)
        break
        default:
          alert('你输错了')
    }
  </script>
</body>
</html>